Process of preparing laminated material



May 10, 1938. c. R. ENSMINGR 2,117,085

PROCESS OF PREPARING LAMINATED MATERIAL Filed sept. as, 193s ATTORNEY.

Patented May 10,' 1938 UNITED STATES PATENT. oFFlcE PROCESS F PBEPARING LAMINATED v y MATERIAL p George R. Ensminger, New Brunswick, N. J., as-

signor to E. I. du Pont de Nemours a Company, Wilmington, Del., a corporation of Delaware Application September 28, 1933, Serial No. 691,343

4 Claims. (Cl. 154-2) This invention 'relates to a laminated material sembly that material improvement; in rust resistand more Particularly a laminated material havance and adhesion of top coat finishes are effected. ing plies of metal and wood. A further object is a method of coating the metal The construction material commonly known as sheet of the laminated structure prior to its union 5 wood veneered metal is composed of a plurality of withthe plywood with a material which will withi layers of wood to which is attached a sheet of stand forming operations.` Afurther object is the metal forming the outermost surface. This strucprovision of a practical and economically feasible ture is produced by means of an adhesive such as commercial process for treating the sheet. metal glue as applied between the several laminations layer'of the plywood veneer structure. Further and therwhole is then subjected to heat and presobjects will appear hereinafter. 10

Sure t0 form a COmDaClJ unit. The productris These objects are accomplished by the use of useful in truck body construction and similar a primer coat preferably of the baking type apstructures where reduced weight combined with plied to sheet metal, either treated or untreated, high strength is desirable. prior to uniting the metal sheet to the plywood l5 Wood veneered metal, the outer layer of which v assembly. 15 is composed of ordinary sheet steel or other metal In the attached drawing Figure 1 represents subject Ato corrosion on exposure is defective in a sheet of metal coated on both sides with a that it cannot be stored for any substantial period primer prior to being cemented to the plywood prior to construction and finishing the truck body, base of the assembly. In Figure 1 A indicates a 24) etc. During normal storage periods considerable metal sheet such as auto body steel coated on 20 rusting occurs, this factor being obviously detriboth sides with a primer B and B as applied prior mental to a satisfactory ultimate decorative and to forming the completed veneered metal strucprotective nish made in accordance with any of ture represented by Figure 2. the finishing Systems known in the art. Figure 2 represents an assembly wherein two I5 Numerous attempts have been made to elimisheets of primed metal have been applied te e 25 nate this defect. Prior to uniting the plywood to Sheet of plywood, A representing the Sheets of the metal sheet the metal has been treated with metal, B and B, the primer coating and C and D certain chemical reagents designed to improve rust the plywood resistance. Such treatment includes galvanhealing and bonderiting, the Iirst being a t nrlefdcoatinils prefelabtly of 11mg xakng 30 process wherein the metal is dipped in molten 'ype u an ry coa ngs are no prec e .X- Zinc and then annealed, the second being a proc ample 1, following, illustrates an oil type coating ess wherein the metal is dipped in a hot bath of which has been found suitable' a solution of iron and manganese phosphates Example 1 ...01'1 type primer 40 This invention has as an object the provision Iamp time iit 6'48 40 of a wood veneered metal of improved resistance P milelra .fp r S"` 5'10 to corrosion during an extended storage period. Cgi" a 01 (ll 7'57 Another object is the provision of a wood veneered Bl na'im 'i'l 2'45 metal of improved anchorage for the ultimate own nSe-e o decorative and protective nish coats which will 1D0 00 45 retain 'this property for long periods after the l application of the top coat without peeling or In the above, the pigment is mixed thoroughly cracking tendencies. Another object of the inin the grinding vehicle and put through aroller vention is a process of so treating the metal sheet mill or a buhrstone mill to eiect proper disperprior to uniting to the other elements of the assion. To this base then, other ingredients are 50 added and thoroughly mixed as in the following proportions:

Intimate formula Percent Above base 63.96 Japan varnish* 9.10 Turpentine 4.00 Mineral spirits 22-94 *The .l'npan varnish is prepared according to standard practice well known in the art and comprises essentially the following ingredients:

Percent Rosin 7. 5

Glycerine 0. 7

Copal 211m 4.6

Linseed oil 15. 2

Drier (red lead and lead acetate) 2. 7

China-wood oil 8. 7

Turpentne 15. 8

Mineral spirits 44. 8

Coatings other than the oil type primer described in Example I may be used such as coatings based on pyroxylin or synthetic resins (phenol-formaldehyde, polyhydric alcohol-polybasic acid resin, etc.). A primer of the baking type is, however, preferable because oi' its general superiority in anchorage for top coats, its resistance to rust and its durability. Example II, following, is illustrative of a synthetic resin primer of the baking type.

Example II Percent Iron oxide 8.22

Lamp black 1.59

`Asbestine 3.78

China clay 4.73

Tale--- 3.78

Litharge .35

Synthetic resin 11.82

Hi-ash naphtha 20.85

Mineral spirits 18.26

Toluene 26.62

*The synthetic resin ingredient in this composition is a reaction product of:

Percent Glyccrol 19.3

Linsecd oil acids 29.6

Plitlmlic anhydride 37.6

China-wood nil 13.5

ioofo This resin is prepared by charging the above ingredients into an aluminum kettle tted with a mechanical stirring device and a thermometer. The batch was heated up to 225 C. in one hour and held at this temperature until an acid number of 30 was reached, stirring being maintained throughout the run. The heating cycle was about 4-6 hours.

This primer is preferably baked at 160 F. for two or three hours. The primer is preferably applied by dipping.

Figure 2 in the drawing illustrates a composite structure including primed metal laminations on both sides. This completed product is manufactured according to the methods known in the art in which an adhesive is applied to the several surfaces ofthe lamination, the various layers assembled, as indicated, and the wholesubjected to heat and pressure to form a compact and unified structure.

Where storage of the metal sheet is Kot contemplated and the assembly is to be made immediately, the sheet may be coated with the primer on only one side, thus providing adequate rust resistance to the exposed surface and insuring suitable anchorage for the finish coats. In this instance, then, in referring either to Figure 2 or Figure 1 the coating represented by B' is omitted. includes structures where but one primed metal sheet is cemented to a single thickness oi' wood or to a single thickness of plywood. To provide for differences in the coefficient of linear expansion between the wood and metal laminations. a strip of fabric coated and impregnated with an adhesive may be placed between the metal and wood surface.

The use of the primer coat on metal sheets which have been previously chemically treated as, for example, by galvannealing or bonderiting" is also within the scope of the present invention. Galvannealed metal is defective in anchorage for thev protective and decorative top coats, which defect is eliminated by the use ot the primer coat particularly that of the baking type. The use of the primer coat likewise is superior to the use of bonderited metal, in the superior anchorage for the top coats as well as in rust resistance. Other modifications of the process will be apparent to those skilled in the art in which the type of construction illustrated in Fig. 2 is of great value in the manufacture of truck bodies, railway coaches, etc., the improvements aiorded by the use of a primer as indicated adding materially to the flexibility of the process and the anchorage and rust resistance of the finishing coats.

Wood veneered metal is manufactured accordingvto processes well known in the art. A plurality of wood sheets are cemented together by the use of adhesives applied by the layers of wood. A sheet of metal such as auto-body steel is alxed to one or both surfaces of the plywood in the The process of the present invention Y same manner and the whole assembly then subjected to heat and pressure to form a contact for lniform structure. The adhesive may be applied to the wood laminations and to the metal sheets by brushing or dipping, preferably brushing. If'

an adhesive such as glue is used the unified structure is permitted to cool in the press since this type of adhesive sets up in this manner. If an adhesive such as phenol-formaldehyde resin is used, the adhesion is gained by chemical change that is, curing of the resin and cooling in the press is therefore unnecessary. Animal or vegetable glues, casein, and certain synthetic resin adhesives may be used. 'Ihe synthetic resin-nitrocellulose adhesives of the copending application of Donald Edgar, Serial No. 658,270, iiled February 23, 1933, may be used. Polyhydric alcohol-polybasic'acid resins, phenol-formaldehyde resins, and pyroxylin adhesives may be used.

In the manufacture of wood veneered metal it is frequently necessary to store the metal sheets forming the outermost layer of the structure for varying periods before use in the assembly. I'he final product with the metal sheet cemented to the plywood base but with its surface exposed may likewise be stored for considerable periods before use in construction, for example, of truck bodies. During these storage periods, a sheet metal surface is exposed to rust and in general affords an undesirable condition for the application of nishing coats, thus requirnga further treatment immediately previous to application of they veneering coats, a treatment which is obviously expensive in time, labor, and

money. The number of methods which have been developed in an attempt to overcome this indicate the importance of the problem, but all of the methods hitherto employed suffer from at least one of the two defects of inadequate resistance to corrosion or inadequate anchorage for further coatings. The use of a primer coat, and particularly the use of a baking primer coat provides a process which avoids these defects. The trouble and expense incident to a chemical treatment of the metalsheet to reduce rusting during storage is eliminated although the use of such treatments in combination with a primer coat is not excluded from the scope of this present invention. The improved wood veneered metal of the present invention provides a satisfactory base for the application of finishing coats in contrast with the previous methods which did not aord adequate anchorage. Ordinary auto body steel, when coated with the primer, affords a satisfactory base for the wood veneered metal product. The uncoated material is quite prone to rust even on relatively short storage periods, but a coated material may be stored for extended periods without adverse effects.

The baking primer compositions shown in Examples I and II are suiiiciently flexible to withstand forming operations so that the sheet metal may be coated therewith, stored until ready for use, and then applied to the laminated wood structure in the desired form. This process which provides for the application of the primer to the metal sheet separately followed by a baking operation thus affords a means of utilizing a baked coating with its advantages in superior rust resistance anchorage forilnishing coats and general durability. A baking primer cannot be utilized after the assembly of the metal and plywood because the wood cannot stand the heat required to bake the primer eii'ectively.

'I'he use of the primer coating in combination with the other elements of wood veneered metal structure simplies the final finishing operations in the construction of truck bodies, railroad coaches, etc., in that the base for the nshing coats is already in place. The method ofthe present invention is economically advantageous in that chemical pretreatment of the metal is not required. 4This permits the use of ordinary auto body steel. 'I'he use of the primer coat on the metal sheet has the further advantage in that the proper primer may be applied thus reducing the chance for unsatisfactory adhesion of iinishing coats applied after the laminated structure has passed from the hands of the manufacturer.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specic embodiments thereof except as de ined in the appended claims.

I claim 1. In the process of preparing laminated material in which at least one metal sheet is joined to wood by means of an adhesive, the improvement which comprises the step of applying a priming coat to the surface of the metal to be in contact with the adhesive, said priming coat being selected from the class consisting of alkyd resins and primers of the oil type.

2. Process of claim 1 which includes the step of baking the priming coat.

3. Process of claim 1 which includes the step of coating both surfaces of the metal with the primer.

4. Process of claim 1 which includes the step of dipping the metal in the priming composition.

GEORGE R. ENSMINGER. 

